1. Field of the Invention
The present invention relates to a magnetic memory device and a magnetic memory device driving method for recording and reading information on and from a magnetic memory device and a magnetic memory including a magnetic memory device.
2. Description of the Related Art
Information devices such as a computer use a high-speed and high-density DRAM (dynamic random-access memory) as a random access memory.
However, the DRAM is a volatile memory which can return information only as long as energizing power is applied and hence a nonvolatile memory whose stored information is undisturbed by removal of operating power has been requested.
A magnetic random access memory (MRAM) capable of recording information based upon magnetization of a magnetic material has received a remarkable attention and it has been developed as nominated nonvolatile memories (see cited non-patent reference 1, for example).
The MRAM is able to record information by inverting magnetization of a magnetic layer of a magnetic memory device located at an intersection point of address wirings with an electric current magnetic field generated from each address wiring when an electric current is applied to two kinds of perpendicular address wirings (word line and bit line).
However, in order to stably hold recorded information, a magnetic layer (memory layer) in which information is recorded needs constant coercive force. On the other hand, an electric current of a certain amount should be applied to the address wirings in order to rewrite recorded information.
Then, as the device comprising the MRAM is microminiaturized increasingly, the thickness of the address wiring also is decreased so that an electric current of a sufficiently large amount cannot be applied to such thin address wirings.
Accordingly, as an arrangement capable of inverting magnetization with application of an electric current of a smaller amount, a magnetic memory having an arrangement using magnetization inversion produced by spin-injection receives a remarkable attention (see cited patent reference 1, for example).
Magnetization inversion produced by spin-injection is a technology in which magnetization is inverted in other magnetic material by injecting electrons spin-polarized through the magnetic material into other magnetic material.
Then, the magnetization inversion produced by spin-injection has an advantage in which magnetization can be inverted with application of an electric current of a small amount even when the device is microminiaturized.
[Cited non-patent reference 1]: NIKKEI ELECTRONICS, 2001, 2, VOL. 12 (pp. 164 to 171)
[Cited patent reference 1]: Official gazette of Japanese laid-open patent application No. 2003-17782
However, in the arrangement in which information is recorded by using magnetization inversion produced by the above-mentioned spin-injection, when ferromagnetic tunnel effect is used to detect magnetization information, since resistance of the device is increased, an insulating layer is broken by a recording voltage, which causes a problem.
Also, in order to freely rewrite information with magnetization inversion produced by the spin-injection, the magnetic memory device should be operated with two polarities by the spin-injection.
However, in order to make magnetizations of the above-described two magnetic materials (magnetic material and other magnetic material become anti-parallel to each other by the spin-injection from a theory standpoint, an electric current of a larger amount is required as compared with the case in which magnetizations of the above-described two magnetic materials are made parallel to each other by the spin-injection.
This becomes a problem that should be solved in order to realize an information memory device in which information can be freely rewritten by an electric current of a small amount.